1. Field of the Invention
The present invention relates to an X-ray analysis apparatus and an X-ray analysis method, which are suitable for, e.g., an energy dispersive fluorescent X-ray analysis or the like.
2. Description of the Related Art
A fluorescent X-ray analysis is one in which a qualitative analysis or a quantitative analysis of a sample is performed by irradiating an X-ray emitted from an X-ray source to the sample and detecting, by an X-ray detector, a fluorescent X-ray which is a characteristic X-ray radiated from the sample, thereby obtaining a spectrum from an energy of the fluorescent X-ray. This fluorescent X-ray analysis is widely used in a process/quality control because it is possible to rapidly analyze the sample without being destructed. In recent years, there is contrived to increase a precision/sensitivity and thus a trace measurement becomes possible, so that there is expected a diffusion as an analysis technique performing especially a detection of a harmful substance contained in a material, a soil and the like.
As this analysis technique of the fluorescent X-ray analysis, there is a wavelength dispersion method in which the fluorescent X-ray is dispersed by a spectral crystal to thereby measure a wavelength and an intensity of the X-ray, an energy dispersion method in which the fluorescent X-ray is detected by a semiconductor detection element without being dispersed to thereby measure an energy and the intensity of the X-ray by a pulse height analyzer, or the like.
Hitherto, e.g., in JP-A-2004-150990 Gazette, there is disclosed a fluorescent X-ray analysis apparatus in which an element analysis of a measurement sample is performed by irradiating a primary X-ray to the measurement sample from an X-ray source through a primary filter, and detecting the fluorescent X-ray radiated from the measurement sample, which received the primary X-ray, by an X-ray detector.
In this fluorescent X-ray analysis apparatus, a reduction in background is contrived and an intensity adjustment of the fluorescent X-ray entering to the X-ray detector is performed by adjusting, by the primary filter, an intensity of the primary X-ray from the X-ray source by selecting a tube electric current of an X-ray tubular bulb and one from among the primary filters of plural kinds.
In the above prior art, the following problems are left.
In a conventional X-ray analysis apparatus, since there is a limitation on an ordinary operation range (maximum X-ray intensity capable of obtaining: maximum obtainable X-ray intensity) in the X-ray detector, there are performed a tube electric current adjustment of the X-ray tubular bulb used as the X-ray source and, as mentioned above by the primary filter, intensity adjustments of the fluorescent X-ray and a scattered X-ray, which enter to the X-ray detector. Here, since a detection lower limit in the X-ray analysis apparatus can be more improved the higher is the intensity of the fluorescent X-ray entered to the X-ray detector, it is set by an adjustment of an intensity of the primary X-ray to be irradiated so as to be capable of detecting approximately with the maximum obtainable X-ray intensity. However, depending on the measurement sample, there is a case where the fluorescent X-ray and the scattered X-ray, which enter to the X-ray detector, are too large and, additionally depending on a case, it is necessary to reduce the tube electric current of the X-ray tubular bulb till such a degree as to exceed an ordinary operation range of the X-ray tubular bulb and, by this, the intensity of the X-ray generating from the X-ray tubular bulb becomes unstable, so that there is an issue that the quantitative analysis by a calibration curve method or the like becomes difficult.
For example, hitherto, in a case where the maximum obtainable X-ray intensity of the X-ray detector is 20×104 cps (Counts Per Second) and the ordinary operation range of the X-ray tubular bulb is in a range from a maximum tube electric current value of 1000 μA to a minimum tube electric current value of 200 μA, if it is supposed that 10×104 cps is obtained at a tube electric current 20 μA in a rough measurement, in a main measurement the tube electric current is set to 40 μA, which is two times, in order to be coincided with the maximum obtainable X-ray intensity of the X-ray tubular bulb, and there is set such that the maximum obtainable X-ray intensity of 20×104 cps is obtained in the X-ray tubular bulb. In this case, the tube electric current does not arrive at the ordinary operation range of the X-ray tubular bulb, by this the intensity of the X-ray generating from the X-ray tubular bulb becomes unstable and, from the fact that, following upon it, an intensity of the detected X-ray becomes unstable, there is a disadvantage that the quantitative analysis is made difficult.